Michael Kelly has revealed more details about his role in new crime drama Criminal Minds: Suspect Behavior.

The actor plays reformed criminal Jonathan 'Prophet' Simms in the new spinoff, which begins tonight at 10/9c on CBS.

"It was a self-defence kill that put him in prison," he told TV Guide. "He killed a child molester, [and] in prison Prophet finds God and becomes a good man."

Kelly explained that Prophet will use his insider knowledge to aid special agent Sam Cooper (Forest Whitaker) and his team.

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"[Prophet starts] helping him solve cases, from the inside, and then I'm asked to join the team," he said. "In the first episode, a big thing happens for my character. He's a provisional agent to begin with, and then things happen. I don't want to give away too much!"

He also suggested that Suspect Behavior will be "grittier" than its parent series.

"We are... solving crimes the same way the original show does, but we're a grittier bunch," he claimed.